Active optical cable with integrated control features

ABSTRACT

An active cable that is configured to communicate over much of its length using one or more optical fibers, and that includes an integrated electrical connector at least one end. The active cable can include a circuit disposed in the integrated cable, the circuit configured to provide pre-emphasis of the second electrical signal. The pre-emphasis can be accomplished by either boosting high frequency content or removing low frequency content from the first or second electrical signals. The active cable can also include circuitry configured to provide equalization of the first electrical signal within the integrated cable. The preemphasis and/or equalization can be fixed, adjustable, or adaptable. The preemphasis and/or equalization can be host selectable via a serial interface of the integrated cable, which can include I2C.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/401,803 filed Apr. 10, 2006, the contents of which are herebyincorporated by reference herein.

BACKGROUND

Communication technology has transformed our world. As the amount ofinformation communicated over networks has increased, high speedtransmission has become ever more critical. High speed communicationsoften rely on the presence of high bandwidth capacity links betweennetwork nodes. There are both copper-based solutions and opticalsolutions used when setting up a high bandwidth capacity link. A linkmay typically comprise a transmitter that transmits a signal over amedium to a receiver, either in one direction between two network nodes,or bi-directionally. An optical link might include, for example, anoptical transmitter, a fiber optic medium, and an optical receiver foreach direction of communication. In duplex mode, an optical transceiverserves as both an optical transmitter that serves to transmit opticallyover one fiber to the other node, while receiving optical signals overanother fiber (typically in the same fiber-optic cable).

Presently, communication at more than 1 gigabit per second (alsocommonly referred to as “1 G”) links are quite common. Standards forcommunicating at 1 G are well established. For instance, the GigabitEthernet standard has been available for some time, and specifiesstandards for communicating using Ethernet technology at the high rateof 1 G. At 1 G, optical links tend to be used more for longer spanninglinks (e.g., greater than 100 meters), whereas copper solutions tend tobe used more for shorter links due in large part to the promulgation ofthe 1000 Base-T standard, which permits 1 G communication over standardCategory 5 (“Cat-5”) unshielded twisted-pair network cable for links upto 100 m.

More recently, high-capacity links at 10 gigabits per second (oftenreferred to in the industry as “10 G”) have been standardized. Asbandwidth requirements increase, potential solutions become moredifficult to accomplish, especially with copper-based solutions. Onecopper-based 10 G solution is known as 10 GBASE-CX4 (see IEEE Std802.3ak-2004, “Amendment: Physical Layer and Management Parameters for10 Gb/s Operation Type 10 GBASE-CX4” Mar. 1, 2004), which accomplishesthe higher bandwidth, despite the use of copper. 10 GBASE-CX4 uses acable, which includes 4 shielded different pairs carrying a quarter ofthe bandwidth in each direction, for a total of 8 differential copperpairs. This cable is quite bulky (typically about 0.4″ or 10 mm indiameter) and expensive to make and cannot be terminated in the field(as can CAT-5 for example). Furthermore, this copper-based 10 G solutionis limited to distances of about 15 m without special efforts.Alternative copper-based 10 G solutions are being developed andstandardized but are likely also to require significant powerconsumption. The primary example is known as 10 GBASE-T underdevelopment in the IEEE (see IEEE draft standard 802.3an, “Part 3:Carrier Sense Multiple Access with CollisionDetection (CSMA/CD) AccessMethod and Physical Layer Specifications Amendment: Physical Layer andManagement Parameters for 10 Gb/s Operation, Type 10 GBASE-T” 2006).This standard uses CAT5e or CAT6A unshielded twisted pair cable fordistances to 55 m and 100 m respectively. However it is expected thatbecause of the extremely complex signal processing required, thisstandard will require circuitry with very high power dissipation,initially as high as 8-15 Watts (per port and thus twice this per link).A lower power variant which only achieves 30 m on CAT6A cable is stillexpected to be more than 4 Watts per port. These high power levelsrepresent both a significant increase in operating costs and perhapsmore importantly, limitations on the density of ports which can beprovided on a front panel. For example, power dissipations of 8-15 Wcould limit port density to 8 ports or less in the space of a typical 1U rack unit, whereas 1000BASE-T and 1 G optical interfaces such as theSFP transceiver can provide up to 48 ports in the same space.Nevertheless, because of the cost of present day optical solutions at 10G, there remains interest in this copper solution.

At the present stage, those setting up the high-bandwidth link willoften weigh the pros and cons of using a copper-based solution versus anoptical solution. Depending on the results of that decision, the systemswill be set up with an electrical port if they decided to proceed with acopper-based solution, or an optical port (often more specifically acage and connector to receiver a standard mechanical form factor opticaltransceiver such as the SFP) if they decided to proceed with an opticalsolution.

BRIEF SUMMARY

Although not required, embodiments of the present invention relate to anactive cable that is configured to communicate over much of its lengthusing one or more optical fibers, and that includes an integratedelectrical connector at least one end.

In one embodiment, an integrated cable includes a first optical fiberwithin the integrated cable, the first optical fiber having a first endand a second end. The integrated cable further includes a firstelectrical connector integrated with the integrated cable, the firstelectrical connector configured to connect with a first electrical portexternal to the integrated cable such that when connected to the firstelectrical port the first electrical connector is configured to receivea first electrical signal and provide the first electrical signal to afirst electro-optical transducer. The first electro-optical transducerdisposed within the integrated cable and coupled to the first end of thefirst optical fiber such that when the first electro-optical transducerreceives the first electrical signal and converts the first electricalsignal into a first optical signal the first optical signal is coupledto the first end of the first optical fiber. The integrated cablefurther includes a second electrical connector integrated with theintegrated cable, the second electrical connector configured to connectwith a second electrical port external to the integrated cable. Theintegrated cable further includes a first opto-electrical transducerdisposed within the integrated cable and coupled to a second end of thefirst optical fiber such that when the first opto-electrical transducerreceives the first optical signal from the second end of the firstoptical fiber the first opto-electrical transducer converts the firstoptical signal to a second electrical signal and provides the secondelectrical signal to the second electrical connector such that whenconnected to the second electrical port the second electrical connectoris configured to provide the second electrical signal to the secondelectrical port. Finally, the integrated cable further includes acircuit disposed in the integrated cable, the circuit configured toprovide pre-emphasis of the first or second electrical signals. Inanother embodiment the circuit configured to provide pre-emphasis of thefirst or second electrical signals is replaced or combined withcircuitry configured to provide equalization of the first or secondelectrical signals within the integrated cable

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings are used in order to more particularly describeembodiments of the present invention. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the embodiments will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates a fully duplex electrical-to-electrical cable;

FIG. 2A illustrates a fully duplex electrical-to-optical cable;

FIG. 2B illustrates a three cable link in which there areelectrical-to-optical cables on each end of the sequence, and a fullyoptical cable disposed therebetween;

FIG. 2C illustrates an electrical-to-optical cable in which the opticalend is coupled to an external optical transceiver;

FIG. 3A illustrates two electrical-to-electrical cables coupled to acable plug end adaptor;

FIG. 3B illustrates more of the mechanical aspects of the cable plug endadaptor of FIG. 3A;

FIG. 4 illustrates two electrical-to-electrical cables with internalpower connections coupled to a cable plug end adaptor;

FIG. 5A illustrates an electrical-to-electrical male-to-female cable;

FIG. 5B illustrates a three cable link that incorporates severalinstances of the cable of FIG. 5A;

FIG. 6A illustrates the configuration of FIG. 3A, except with retimingincorporated;

FIG. 6B illustrates the configuration of FIG. 4, except with retimingincorporated;

FIG. 7A illustrates the configuration of FIG. 5A, except with retimingincorporated;

FIG. 7B illustrates the configuration of FIG. 5B, except with retimingincorporated;

FIG. 8A illustrates a passive electrical-to-electrical copper cable thatincludes an electrical connector that is structured the same as anelectrical connector of the electrical-to-electrical optical cable ofFIG. 1 or FIG. 2A;

FIG. 8B illustrates a view of an example cross-section of the coppercable of FIG. 8A;

FIG. 9 illustrates an active electrical-to-electrical copper cable thatincludes an electrical connector that is structured the same as anelectrical connector of the electrical-to-electrical optical cable ofFIG. 1 or FIG. 2A;

FIG. 10 illustrates an active electrical-to-electrical copper cable thatincludes a power transmission line and that includes an electricalconnector that is structured the same as an electrical connector of theelectrical-to-electrical optical cable;

FIG. 11 illustrates an active electrical-to-electrical copper cable thatincludes a mechanism for transmitting power of the signal carryinglines, and that includes an electrical connector that is structured thesame as an electrical connector of the electrical-to-electrical opticalcable;

FIG. 12A illustrates an active copper cable transmitter integratedcircuit;

FIG. 12B illustrates an active copper cable receiver integrated circuit;

FIG. 13A illustrates a three cable link that includeselectrical-to-electrical copper cables on the ends and an optical cablewith electrical connectors in the middle, in which power is supplied tothe electrical connections in the optical cable using dedicated powertransmission lines;

FIG. 13B illustrates a three cable link that includeselectrical-to-electrical capper cables on the ends and an optical cablewith electrical connectors in the middle, in which power is supplied tothe electrical connections in the optical cable using the signalcarrying lines of the copper cables;

FIG. 14A illustrates a dual link electrical-to-electrical optical cable;

FIG. 14B illustrates a dual link electrical to two single linkelectrical cable;

FIG. 15A illustrates an example 11 pin arrangement of a single linkcable;

FIG. 15B illustrates an example 9 pin arrangement of a single linkcable;

FIG. 15C illustrates an example 20 pin arrangement of a single linkcable;

FIG. 15D illustrates an example 20 pin arrangement of a dual link cable;

FIG. 15E illustrates an example 22 pin arrangement of a dual link cable;

FIG. 16 illustrates a schematic of the internals of one end of a singlelink cable including the electrical connector;

FIG. 17A schematically illustrates the internals of one end of a duallink cable including the electrical connector;

FIG. 17B illustrates another perspective view of the electricalconnector end of FIG. 17A;

FIG. 17C illustrates yet another perspective view of the electricalconnector end of FIG. 17A;

FIG. 18 illustrates a perspective view of an electrical end a singlelink cable in accordance with the principles of the present invention;

FIG. 19 illustrates an SFP to active cable adaptor electrical conversionmapping component;

FIG. 20A illustrates a first view of an SFP to active cable adaptor inaccordance with one embodiment of the present invention;

FIG. 20B illustrates another perspective view of the adaptor of FIG.20A;

FIG. 20C illustrates yet another perspective view of the adaptor of FIG.20A;

FIG. 20D illustrates a final perspective view of the adaptor of FIG.20A;

FIG. 21 illustrate an XFP to active cable adaptor electrical conversionmapping component;

FIG. 22A illustrates a first view of an XFP to active cable adaptor inaccordance with one embodiment of the present invention;

FIG. 22B illustrates another perspective view of the adaptor of FIG.22A;

FIG. 22C illustrates yet another perspective view of the adaptor of FIG.22A;

FIG. 22D illustrates a final perspective view of the adaptor of FIG.22A;

FIG. 23 illustrate an X2 to active cable adaptor electrical conversionmapping component;

FIG. 24A illustrates a first view of an X2 to active cable adaptor inaccordance with one embodiment of the present invention;

FIG. 24B illustrates another perspective view of the adaptor of FIG.24A;

FIG. 24C illustrates yet another perspective view of the adaptor of FIG.24A; and

FIG. 24D illustrates a final perspective view of the adaptor of FIG.24A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention relate to the use of acommunication cable that is exposed at least at one end using anelectrical connection, while communicating over much of its length usingoptical fiber. Thus, those designing or selecting networking equipmentor administrating network nodes need not choose a copper-based solutionor an optical solution in communicating over a network. Instead, thenetwork node need only have an electrical port of some type to therebysupport either copper-based communication or optical communication. Inaddition to network applications, such a cable can support point topoint high speed serial connections such as the transmission ofserialized video data from source to a display. The communication overthe optical fiber may be high speed and suitable for 10 G applicationsand higher. As will described below, cable designs which are purelyelectrical but mechanically and electrically interoperate with theoptical cables described herein may be included as part of a completesystem to provide the most effective solutions over the widest range ofapplications.

FIG. 1 illustrates an integrated cable 100 that has electricalconnections 111 and 121 at both ends. Each electrical connection issized and configured to connect to a corresponding electrical port ateach network node. For example, electrical connector 111 is configuredto connect to electrical port 112 at one network node, while theelectrical connector 121 is configured to connect to the electrical port122 at the other network node. From the external connection viewpoint,it is as though the cable is entirely an electrical cable.

However, upon closer examination of the cable 100 of FIG. 1,communication over at least part of the cable length is actuallyaccomplished via optical fibers. Each end of the cable 100 has opticsthat support duplex-mode optical communications. Specifically, theoptics at each end of the cable 100 include a transmit opticalsub-assembly (TOSA) for transmission of an optical signal over oneoptical fiber and a receive optical sub-assembly (ROSA) for receipt ofan optical signal from another optical fiber. Integrated circuits todrive the transmitting optics and to receive the detected signal areincluded. These ICs may be outside the TOSA or ROSA or may be integrateddirectly in their design. Though the cable 100 is illustrated assupporting duplex-mode in which optical communication occurs in eitherdirection, the cable may also perform communication in one directionconsisting of a single transmitter at one end and a single receiver atthe other.

Referring in further detail to FIG. 1, the cable 100 includes twooptical fibers 131 and 132 integrated within the cable 100. When anelectrical signal is applied to the appropriate connections of theelectrical connector 121 (e.g., through the electrical port 122), thoseelectrical signals are converted by a laser driver and TOSA 123 (or morespecifically by an electro-optical transducer within the TOSA 123) to acorresponding optical signal. As noted, the laser driver may be includedwithin the TOSA. The optical signal is transmitted over optical fiber131 to ROSA 114. The ROSA 114 (or more specifically, an opto-electronictransducer within the ROSA 114) converts the optical signal receivedfrom the optical fiber 131 into a corresponding electrical signal.Typically the optical transducer would consist of a PIN detector and apreamplifier Integrated Circuit (IC), usually with a transimpedanceamplifier front-end design. A limiting amplifier may also be integratedwith the preamplifier or provided separately. The electrical signal isapplied on the appropriate connections of the electrical connector 111,whereupon it is provided to the electrical port 112. While the cable 100may be of any length, in one embodiment, the length is from 1 to 100meters. The cable may support high speed communication range between 1to 10 gigabits per second and beyond.

If the principles of the present invention are to be applied tobi-directional communication, when an electrical signal is applied tothe appropriate connections of the electrical connector 111 (e.g.,through the electrical port 112), those electrical signals are convertedby a laser driver and TOSA 113 (or more specifically by anelectro-optical transducer within the TOSA 113) to a correspondingoptical signal. Once again, the laser driver may (but need not) beintegrated within the TOSA. The optical signal is transmitted overoptical fiber 132 to ROSA 124. The ROSA 124 (or more specifically, anopto-electronic transducer within the ROSA 124) converts the opticalsignal received from the optical fiber 132 into a correspondingelectrical signal. The electrical signal is applied on the appropriateconnections of the electrical connector 121, whereupon it is provided tothe electrical port 122. The cable 100 may additionally include aprotective coating 133 which protects the optical fibers, the optics andportions of the electrical connectors. Finally, though not shown in thefigure, the fiber optic cable would typically include some form ofstrength member such as Kevlar yarn.

In principle, any type of optical fiber (single mode or multimode) couldbe used with the appropriate TOSA and ROSA designs. In some embodiments,however, the use of multimode fiber for links of 100 m and less withshortwave (˜850 nm) VCSEL sources may be desirable. There are severalimportant types of multimode fiber worth considering and distinguishingwhich is preferred in different situations. Of course, as the relativecosts and alternatives associated with each of the multimode fibersolutions changes over time, the considerations referred to below mayalso change.

Presently, a quite cost effective choice for connections at least to 30meters would be a type of multimode fiber generically referred to as OM2which has a core and cladding diameter of about 50 and 125 micronsrespectively and has a minimum overfilled bandwidth (OFL) of about 500MHz·km. While links can be constructed using this fiber for distancesbeyond 30 meters, the fiber would start to add a significant amount ofjitter to the link (discussed generally below) which may be anundesirable tradeoff.

For links longer than about 30 meters, fiber with a tighter tolerance onthe core design but with identical mechanical dimensions may bedesirable. In particularly, a class of fiber generally known as OM3which has a minimum OFL of 2000 MHz·km is available, and would providevery small signal impairment to a distance of 100 meters or more (and ithas conventionally been used for links up to perhaps 300 meters).

Those skilled in the arts will recognize that the distance at which touse a certain type of fiber will be determined by many factors and mayresult in a tradeoff point significantly different than 30 meters.

An important new type of multimode fiber made with organic polymer(plastic) material may prove extremely cost effective for theseapplications because of the simplicity of the termination of a fiberitself. Plastic fibers have been available for many years but havegenerally required very short wavelength sources (about 650 nm) andbecause of their simple step index core design have bandwidths orders ofmagnitude too low for 1 G to 10 G applications. Recently however,designs have been introduced which substitute fluorine for hydrogen inthe polymer structure reducing attenuation at longer wavelength such as850 nm. More importantly, graded index core designs have been realizedwhich provide OFL bandwidths of 300 MHz·km or more which is sufficientfor links of 20 meters or longer.

Of course, the opto-electronic conversion process and the electro-opticconversion process require power in order to convert between optical andelectrical energy. Thus, the electrical connectors supply power from thehost at least one end of the cable 133 to power the opto-electronicconversion. The power connection may be, for example, a 3.3 volt powerconnection. In FIG. 1, for example, the electrical port 112 isillustrated as supplying Power/Gnd connections for conveying electricalpower from the host to electrical connector 111.

Thus, conveyance of information is accomplished largely by means of anoptical signal, while providing electrical connections on both ends ofthe cable. The purchaser of the cable need not even be aware that thecable is an optical cable. In fact, a copper cable could be provided forparticularly short links (perhaps 1 to 5 meters) which emulates thecable 100 of FIG. 1, embodiments of which are described further belowwith respect to FIGS. 8A through 13B.

While a single cable assembly linking two pieces of equipment isprobably the simplest and lowest cost configuration in terms of hardwareand perhaps preferred for shorter links (for example, less than 10meters), it may prove inconvenient to install for longer connections(for example, more than 30 meters). For longer distances, connections ofmultiple cables may be more convenient. In conventional optical links,for example, it is common for a longer length of cable to be terminatedat each end at a patch panel consisting of one or more cable plug endconnectors. A short connection is made from the optical ports on networkequipment at each end of the link to the corresponding patch panel usinga relatively short (from 1 to 5 meter) patch cable. In other cases, evenmore complicated connections are used involving as many as 4 to 6connections.

While some embodiments of potential applications of the presentinvention could be served by a single cable, variations which wouldallow the connection of at least three cables would be of great utility.There are several possible methods by which the present cable may beinterconnected to other such cables or other variants to be described,all of which being encompassed within the principles of the presentinvention. The various embodiments have different relative advantages.

FIG. 2A illustrates an integrated cable 200 in accordance with anotherembodiment of the invention in which the cable 200 may be used as onelink in a multiple link connection. The integrated cable 200 of FIG. 2Ais similar to the integrated cable 100 of FIG. 1, except that theintegrated cable 200 has an electrical connector 211 on only one end ofthe cable for connection with the electrical port 212, and an opticalconnector 221 on the other end of the cable. The optical connector 221is configured to permit the cable to receive optical signals from otheroptical cables through optical fiber 231 using connectors 221 and 222,and transmit optical signals from optical fiber 232 through the otheroptical cable also using connectors 221 and 222.

In the illustrated embodiment of FIG. 2A, the optical connector 221 isillustrated as a standard LC optical connector (see ANSI/TIA/EIA 604-10.“FOCIS-10 Fiber Optic Connector Intermateability Standard” October 1999for more information concerning the standard LC optical connector).However, any optical connection may suffice including, but not limitedto, SC optical connectors (see IEC61754-4 “Fiber optic connectorinterface Part 4: Type SC connector family” Ed 1.2, 2002-2003 for moreinformation concern the standard SC optical connector) as well as otheroptical connections, whether now existing or to be developed in thefuture. While the cable 200 may be of any length, in one embodiment, thelength is from 1 to 5 meters.

The cable illustrated in FIG. 2A may be used in a 3 cable configurationas shown in FIG. 2B where an electrical to optical cable 200A isconnected to an optical cable 201 and then to a second optical toelectrical cable 200B. The electrical to optical cables and optical toelectrical cables may be referred to herein as “E-O” cables. In oneembodiment, the E-O cables 200A and 200B are each instances of the cable200 illustrated and described with respect to FIG. 2A. The optical cable201 may, but need not, be a standard optical cable.

Thus, electrical signals received from electrical port 212B of the righthost in FIG. 2B may be received by the electrical connector 211B of theE-O cable 200B, converted into an optical signal using the TOSA andassociated laser driver of the E-O cable 200B, pass through the E-Ooptical interface 232B defined by the connection between opticalconnectors 221B and 231B, pass through the optical cable 201, passthrough the optical interface 232A defined by the connection betweenoptical connectors 231A and 221A, through the E-O cable 200A as anoptical signal, to finally be received by the ROSA of the E-O cable200A, whereupon the corresponding electrical signal is received by theelectrical port 212A of the left host through the electrical connection211A.

Conversely, electrical signals received from electrical port 212A of theleft host in FIG. 2B may be received by the electrical connector 211A ofthe E-O cable 200A, converted into an optical signal using the TOSA andassociated laser driver of the E-O cable 200A, pass through the E-Ooptical interface 232A defined by the connection between opticalinterface 221A and 231A, pass through the optical cable 201, passthrough the optical interface 232B defined by the connection betweenoptical connectors 231B and 221B, through the E-O cable 200B as anoptical signal, to finally be received by the ROSA of the E-O cable200B, whereupon the corresponding electrical signal is received by theelectrical port 212B of the right host through the electrical connection211B. In alternative embodiments, the multi-cable link illustrated inFIG. 2B may be extended to consist of multiple lengths of standardoptical cable to extend the link to beyond 3 cables.

The E-O cable 200 could have specifications on the optical input andoutput such as the minimum and maximum transmitted modulated power andthe minimum and maximum acceptable receive power. These could either becustom specifications to enable a particular range of links with givenfiber types. Alternatively, the optical interface of this cable couldcomply with one or more existing or future optical standards formultimode or single mode fiber connections.

One example would be the IEEE 10 G BASE-SR standard which allowstransmission of up to 300 meters on some grades of multimode opticalfiber. This also allows a link as shown in FIG. 2C where one end 263 ofthe E-O cable 200C is connected to a first piece of network equipment260 by connecting electrical connection 261 of the cable 200C to anelectrical port 262. The E-O cable 200C may be, for example, oneinstance of the E-O cable 200 of FIG. 2A. The other end 265 of the E-Ocable 200C may be configured as an optical connector that is connectedto an optical transceiver 266, which has an electrical interface 267with a second piece of network equipment 268. Thus, in one embodiment,the E-O cable 200C may interoperate with existing optical transceiverssuch as, for example, the SFP (see Small Form-factor Pluggable (SFP)Transceiver Multi-source Agreement (MSA), Sep. 14, 2000. Also, TNF-8074iSpecification for SFP (Small Formfactor Pluggable) Transceiver Rev 1.0May 12, 2001), XFP (seehttp://www.xfpmsa.org/XFP_SFF_INF_(—)8077i_Rev4_(—)0.pdf), XENPAK (seehttp://www.xenpak.org/MSA/XENPAK_MSA_R3.0.pdf), X2 (see http://www.x2msa.org/X2_MSA_Rev2.0b.pdf) or XPAK transceivers, as long as the cable200C followed a consistent set of optical specifications suitable forthe transceiver type. The configuration shown in FIG. 2C could alsoinclude one or more lengths of optical fiber with standard connectors,with the number determined by the optical link budget to which the E-Ocable and optical transceiver comply.

Referring for a moment back to FIG. 1, although the cable 100communicates over much of its length using optical signals, the cable100 is connected externally using electrical connectors at both end.Thus, the electrical to electrical (E-E) cable 100 illustrated in FIG. 1does not have to meet any external optical specification. This is agreat advantage to achieving low cost. These inventive principles makeit possible to retain this advantage in multiple cable links in a numberof possible ways.

In one embodiment, the cable 100 is used in a three link system of E-Ecables by connecting the cables 300A and 300B passively with a cableplug end connection 320 as shown in FIG. 3A, or passively with any othermale to male adaptor. The cables 300A and 300B may each be instances ofthe cable 100 of FIG. 1. For instance, the cable might have a malegender connector (portion 306 of cable 300A, and portion 311 of cable300B) with the corresponding host receptacles 301 and 310 each being afemale connector. In this case, a cable plug end connector 320 would becomprised of two female receptacles 321A and 321B with the receiverconnections of one cable (e.g., cable 300A) connected to the transmitterconnections of a second cable (e.g., cable 300B), and vice versa. Thefemale receptacle 321A receives the mail connector 304A of the cable300A, whereas the female receptacle 321B receives the mail connector304B of the cable 300B. Additionally, low speed control or indicatorlines 323 may be used to supply power and low speed control data to theappropriate connection.

One consideration about the above described connection is that itrequires that power be available to the optics in the connected ends ofthe E-E cable. In one embodiment of the E-E cable, there is no copper orother electrical conductor and thus no power connection between thecable ends, with the power for each end being supplied by the hostsystem at each end. In one embodiment, power is delivered to the cableends in one or more of the following two ways.

FIGS. 3A and 3B illustrated a cable plug end adapter for connecting twoE-E cables of the type illustrated in FIG. 1. The power for the twoconnector ends, 303 and 312 is provided separately to the cable plug endadapter. As one example, shown in FIG. 3A, a chassis 325 may be providedwith a single power connection and power supply 326 which in turnssupplies power to one or cable plug end adapters. FIG. 3B shows anotherexample of such a powered set of receptacle to receptacle adapters 350where the inputs (e.g., input 360) and outputs (e.g., 361) (note thatthe inputs and outputs are reversible) are arranged on the same side ofthe chassis. The adapter 350 itself receives power via power line 352being fed into the adaptor 350 at portion 351.

A second method for providing power is illustrated in FIG. 4, which issimilar to the structure described with respect to FIG. 3A. However, inthis case, E-E cables 400A and 400B are provided. Either or both of thecables 400A and 400B may be the same as that described with respect toFIG. 1, except that at least a pair of electrical conductors (411A and412A in the case of cable 400A, or 411B and 412B in the case of cable400B) is provided in the cable along with the optical fibers. Theseconductors 411 and 412 may either directly connected to the powerconnections on either end or in order to provide isolation between thetwo host ends in the normal connections. Pins may be provided separatelyfor the near-end and far-end power connections. In one example, theconductor 411 may be a ground conductor, whereas the conductor 412 maybe a power conductor.

An alternative form of the E-E cable could be used to concatenate two ormore E-E cables without the need for a separate adapter/connector. Thisalternative E-E cable 500 is illustrated in FIG. 5A, and thecorresponding 2 cable configuration shown in FIG. 5B. The E-E cable 500shown in FIG. 5A has a male plug connector 506 on one end 505 (i.e., theleftward illustrated end), which would be connected to the femalereceptacle 501 on the leftward illustrated host system, and containstransmit and receive optics in the form of a TOSA and a ROSA. The otherend 503 (i.e., the rightward illustrated end) of the cable would alsocontain transmit and receive optics coupled to the optical fiber, alsoin the form of a TOSA and a ROSA. This right end 503, however, would beconfigured with the receptacle female gender connector 507 which wouldfunction like a host connector, so that further cables may be attachedto the cable 500 in a similar manner as those cables would be attachedto a host connector. In one embodiment, the cable 500 might be arelative short “patchcord” lengths of approximately one to five meters.The electrical conductors 520 and 521 are provided in order to providepower to the remote receptacle end 503 (the rightward end) from the hostsystem (illustrated on the left). Referring to FIG. 5B, an instance 500Aof the cable 500 of FIG. 5 may be combined with another cable 501 (whichis similar to the cable 100 of FIG. 1) to form a series of two cables.Furthermore, a series of three or more cables may be accomplished byconnecting multiple instances of the cable of FIG. 5A, with the cable ofFIG. 1. For instance, if three cables were to be used, two instances ofthe cable of FIG. 5A may be combined with one instance of the cable ofFIG. 1. In that case, the center cable may be of a relatively long runof, for example, from ten to one hundred meters.

It may prove advantageous to provide separate power supplies for thenear end (host side) and far end of a cable which incorporateselectrical power conductors for a number of reasons. One reason is thedesire to provide a degree of isolation between the interconnectsystems. The second reason is to limit the supply requirements of thenear end connection used in the majority of connections.

Finally, and probably most important is the desire to overcome somedegree of voltage drop along the electrical conductors particularly islight weight, thinner conductors (higher gauge) are used. The use of ahigher far end supply voltage may take one of two forms. The first isthe use of a slightly higher supply voltage to overcome the conductorvoltage drop. As a particular, the active devices in each end of thecable might require a supply voltage of +3.3V±5% (3.145 to 3.465V). Inthis case, requiring a 3.6V±5% (3.42 to 3.78V) on the far end supplyconnection would easily overcome the voltage drop expected in patchcordsof 5 m or less with typical copper wire gauges. The second case is wherethere is a need to overcome losses in longer cable runs or to supply alarger amount of power to equipment at the cable end (for exampleadapters with retimers or even remote disk drives). In this case, it maymake sense to use a much higher voltage (say about 40 Volts) where theresistive current loss would be much less. When such high voltages areused, the power must be converted down to lower voltages at the far endthrough the use of a switching power supply for example.

In any of the above described systems, it might be advantageous tospecify the characteristics of various elements in the system in termsof the amount of signal timing jitter they add in order to limit thetotal jitter of the link to a value which can be handled by the circuitelement which ultimately recovers the clock and retimes the signal.Jitter refers to the error in the time position of the digital datatransitions and can have numerous sources some of which can becharacterized as random and others which result in deterministic,usually data dependent errors in timing.

The above-described methods and mechanisms of linking cables willinvolve more interfaces (including the connectors, the laser driver andreceiver ICs and the lasers and fibers themselves) that can add jitterto the transmitted data signal as compared to a single cable. Thus,meeting a reasonable jitter budget will generally be significantly moredifficult in a multi-cable system as described than in a single cable(which could even be tested for its total jitter contribution in thefactory).

It is possible to overcome potential jitter limitations by incorporatingretiming circuits into the link. For example, a clock and data recoverycircuit will eliminate jitter beyond a given frequency effectivelyresetting the jitter budget in this type of system. Although retimingcircuits could be incorporated in the cable plug end adapters (or otheradaptor for each direction of each duplex link described above andillustrated in FIGS. 3A, and 4, where the power for the optics and theretiming circuit would be supplied locally or from the patchcord-cablerespectively. An example of such a system is shown in FIGS. 6A and 6B,in which one or more adapters are incorporated in a single chassis, andusing a single Integrated Circuit (IC) that incorporates more than onechannel of retiming circuits.

Specifically, FIG. 6A illustrates a configuration that is similar to theconfiguration of FIG. 3A, except that there is a retiming circuit 601A,601B or 601C within the cable plug end adaptor and interposed within thecorresponding electrical channel within the cable plug end adaptor. Forinstance, retiming circuit 601B is interposed between active cables 600Aand 600B to provide for appropriate jitter reduction through retiming.Actually, there are two retiming circuits represented by the retimingcircuit 601B, one for each direction of communication. The same can besaid for retiming circuits 601A and 601B. Here, power is supplied by thecable plug end connection itself. Mechanisms for retiming are known inthe art and thus will not be described in detailed herein.

FIG. 6B illustrates a configuration that is similar to the configurationof FIG. 6A, except that now power conductors are provided in one or bothof the active cables 700A and 700B to provide power to the cable plugend connector. Power from one or both of these connectors could be usedto power the retiming circuits 701A, 701B and 701C (once again, sixretiming circuits total), which operate to retime the electrical signalsin the corresponding channel. For instance, retiming circuit 701B isinterposed between active cables 700A and 700B to provide forappropriate jitter reduction through retiming.

Similarly, a retiming circuit could be added to the plug-receptacle typepatchcord described in FIG. 5A. This embodiment is illustrated in FIG.7A, and the associated 2 cable connection of FIG. 5B using thisarrangement is shown in FIG. 7B. For instance, referring to FIG. 7A,electrical signals received from the female electrical connector 704 areretimed by retiming circuit 710, whereas electrical signals to betransmitted onto the female electrical connector 704 are retimed byretiming circuit 711.

As described in the some of the implementations of the copper basedsolution, the cable may also include a mechanism for supporting adaptiveequalization of an input high speed electrical signal to reduce totallink jitter, a mechanism for providing host selectable equalization ofan input high speed electrical signal to reduce total link jitter, amechanism that provides pre-emphasis of an output high speed electricalsignal to reduce total link jitter, a mechanism for providing hostselectable pre-emphasis of an output high speed electrical signal toreduce total link jitter. Different host systems may require differentdegrees of equalization and/or preemphasis because of the particularlength or other nature of the electrical interconnect between the cablereceptacle and the next IC elements. The integrated cable may supportpredefined limits of added deterministic and total jitter of a highspeed signal, where such limits may be chosen to allow concatenation ofup to 3 cables.

Another means of controlling jitter is non-linear jitter compensationwhich detects and adjusts edges of particular transitions (see UnitedStates Patent Publication No. 20050175355). This method is particularlywell suited for compensating for known fixed deterministic jittersources such as those arising from a particular length of host PCBtrace.

It should be noted that while most of the jitter reduction techniquesdescribed address the jitter introduced by channel limitations on thehost system or on a copper based cable, they may also be usefullyapplied to compensate for non-idealities of the optical transmitter orreceiver (such as those do the non-linear characteristics of the lasersource). They may also be used to compensate for the channelcharacteristics of the fiber itself. Depending on the type of fiber usedand the length employed relative to it's total frequency bandwidth, thecompensation may be for a simple frequency rolloff or for the morecomplex multiple peaked impulse responses seen in typical multimodefiber due to differential mode delay.

Cables in accordance with the principles of the present invention mayalso include additional functionality. For instance, the cable mayinclude a mechanism for confirming whether or not a full duplexconnection is present (e.g., by transmitting and receiving a relativelylower optical power level within Class 1 eye safety limits over eitheror both of the first optical fiber and the second optical fiber), amechanism to reduce or shut-off optical power whenever a full duplexconnection is not confirmed, and/or a mechanism to keep the opticalpower reduced or off until the presences of a full duplex connection isverified.

The electrical connector may include connections for a loss of signal(LOS) indication, a fault indication, a link disable control signal,presence indication of the integrated cable to a host system that isassociated with the first or even second electrical port, an interruptsignal, a reference clock input, low speed serial data interfaces and/orany other connections for control of the cable.

The low speed serial data interface may be configured for use in controlof the first electro-optical transducer, may be part of a system for thetransmission of out of band data, may be configured to read or writedata to nonvolatile memory in the optics portion of the cable, and/ormay be used for one or more functions selected from the following list:serial identifier codes, customer security codes. Customer securitycodes could be provided to specially allow only host qualifiedimplementations of the cable and to detect outright counterfeit parts.Diagnostic information, which would be dynamically updated in volatilememory could be provided over the same serial interface. The serialinterface may also be used for factory setup of the device to loadnon-volatile data to an internal EEPROM, FLASH memory or set of fusiblelinks in the laser driver and/or receiver IC. The serial interface maybe any serial interface, whether not existing (such as SPI interface orI2C interface) or whether to be developed in the future.

The cable may also include its own eye safety measures including amechanism to disable one or more optical transmitter within theintegrated cable if the integrated cable is physically severed such as,for example, when the nominal transmitted power may be greater than theIEC class 1 eye safety limit, a mechanism to transmit optical power ateye safe levels if the integrated cable is physically severed, and/or amechanism to assert a fault signal if the integrated cable is severed.Furthermore, the eye safety circuit could be used to reassert the linkif the shutoff were caused by a reversible cause such as the shutoff ofpower to the remote end.

One particular mechanism, which might be integrated in the cable, is theOpen Fiber Control (OFC) system developed as part of the Fibre Channelstandard (see ANSI X3.230-1994 section 6.2.3 pp 42-48). In fact, aconsiderably simplified version of the OFC protocol could be used sinceOFC must deal with two independent transceivers and must functionproperly if a non-OFC transceiver is connected to an OFC device. In thecase of an active cable where both ends are controlled, this situationcannot occur. In any case, the eye safety features in the cable may bedesigned to function in the event of any reasonable single faultcondition.

The cable may include at least one electrical conductor spanning thelength of the integrated cable. As previously mentioned, this electricalconductor may be used to transmit electrical power from one end of thecable to the other end of the cable. However, alternatively or inaddition, there may be electrical conductors for transmitting low speedserial data from one end of the integrated cable to the other end of theintegrated cable. Furthermore, the cables included for transmittingelectrical power may be simultaneously used for transmission of lowspeed serial data.

FIG. 8A shows perhaps the simplest implementation of a copper cable 800designed to interoperate with the optical cables previously described.In this example, the link is entirely passive, with a pair of copperconductors (pairs 831 and 832) carrying the two duplex data streamsbetween each connector. The copper conductor pair couple may be in theform of a shielded or unshielded twisted pair (as used in CAT-5 cabling)or in the form of a single ended or differential coaxial cables. Forsuch a high bandwidth link, it would very advantageous to also includean overall cable shield 835, tied to chassis ground of at last one hostto limit electromagnetic emissions. FIG. 8B illustrates a cross-sectionof what the cable 800 might look like. The other components of the cable800 may be structured the same as described above for the cable 100.

For a 10 G data rate and a reasonable size cable, the possibletransmission length without special means in the host system would bevery short, perhaps on the order of 1 meter of length. To improve thetransmission length, active elements could be incorporated into thecable design as is illustrated into FIG. 9. In FIG. 9, cable driver ICs913 and 923 and cable receiver ICs 914 and 924 are included in the cableends. The functionality of these ICs will be described further below.Otherwise, the cable 900 of FIG. 9 may be structured the same asdescribed above for cable 800 of FIG. 8.

The same considerations for supplying power over the cable discussedpreviously apply to the copper variants as well; however there are somedifferences in implementation. For example, if needed, the copper signalconductors in FIG. 8 could be adapted to apply a supply voltage.Alternately, a separate pair of conductors for power could be includedas shown in the cable 1000 with active cable drivers 1013, 1014, 1023and 1024 illustrated in FIG. 10. Since the need for a remote power isparticular to two or more cable connections, FIG. 10 shows the remoteend of the cable with a female receptacle 1004 to be used as apatchcord. In addition to the copper signal pairs 1031 and 1032, acopper power pair 1036 is provided for providing power from one end ofthe cable 1000 to the other. A shield 1035 is also provided for EMIprotection.

FIG. 11 illustrates the same cable functionality as FIG. 10, but wherethe power is supplied to the remote end over the signal pairs, ratherthan having a dedicated power pair. Specifically, power from one end ofthe cable is provided into the copper twisted pair, and pulled from thattwisted pair at the other end of the cable.

FIGS. 12A and 12B illustrates some of the useful features which might beincorporated into the ICs in a copper active cable design. FIG. 12Ashows the transmitter Integrated Circuit (IC). The first block in thisIC would provide equalization to compensation for high frequency loss inthe host board traces. Such equalization could be fixed, host selectablevia a serial interface or automatically adaptive to the hostimpairments. The next block shown is jitter precompensation. In thisrelatively new technique, particular data transitions which tend to havethe most significant associated deterministic timing errors (jitter) aredetected and fixed small time delays are added to compensate. This canbe used to compensate for both host board impairments as well as for atleast a portion of the bandwidth impairment of the copper cable. Thenext block is a limiting function which restores the signal levelsamplitudes which vary according to the host ICs and may have beenfurther attenuated by the host transmission lines. The final blockprovides preemphasis to the high frequency content of the transmittedsignal to overcome the larger loss on the cable of these highfrequencies. This is well known technique and gains of 12 dB or largermay be used. The amount of gain can be adjusted at factory setupindividually to match the particular length of the characteristics ofthe copper cabling.

Preemphasis is accomplished by either boosting the high frequencycontent or removing low frequency content. In either case, the resultingelectrical waveform which results tends to show a large overshoot inafter the transmission edge.

It should be noted that only a subset of the functional blocks may beincluded in the cable driver IC represented in FIG. 12A particularlysince some of their effective functionality is overlapping.

Also shown in FIG. 12A, but likely not fully integrated into the ICitself would be optional circuit elements for combining a DC powerconnection into the signal power cable. The most straightforward meanswould be the use of a bias T where a large inductor or chain ofinductors and other matching components is used to couple in DC currentinto the copper cable without significantly perturbing the highfrequency characteristics of the high speed transmission lines.

FIG. 12B shows the elements which could be included in an active cableIC receiver for the copper implementations of the cable. The elementsfollow somewhat in the reverse of the driver IC, but with importantdifferences.

Beginning on the left of FIG. 12B, where the copper pair or coax isreceived from the main length of the cable, there is an optional DC biascircuit to recover far end power from other cable end. This power can beused to supply the receiver IC itself and/or other elements in thatcable end, or even components to which the remote cable end is attached,such as a powered adapter for connecting a following length of cable.

The next block shown, completely within the IC, is adjustableequalization. This block of equalization is provided to compensate forthe cable high frequency rolloff, rather than the host PCB traces in thecase of the driver. As in the case of the driver, it may provide fixed,adjustable or adaptive equalization. Adjustable but factory setequalization is of particular interest because the cable length andcharacteristics will be established at the time of the cablemanufacture.

Following optional equalization, a limiting amplifier restores the zeroand one levels to uniform amplitudes. In most such receivers, it isnecessary to maintain an appropriate DC level at the circuit inputs tomaintain proper duty cycle operation. This is typically implemented asshown by a DC restore loop which also establishes a low frequency cut-onof the high speed channel, which must be chosen appropriate for theminimum data rate and coding scheme.

Finally, for driving the host PCB traces at this end of the cable, anoutput driver is provided with optional preemphasis. In the case of thereceiver, the preemphasis would be provided to help overcome highfrequency losses on long PCB traces which can add significant jitter at10 G operation. The preemphasis could be fixed, adjustable withadjustment at the factory or based on host control information on theexpected loss characteristics of the PCB channel.

FIGS. 13A and B illustrates what might be the most economicalarrangement to achieve the advantages of a three cable connection. Inthis case, copper based patchcords are used for relatively short (1-5meters) connections from host equipment to patchpanels, where they wouldjoin to a long length (5-100 meters) of fiber optic based active cable.In addition to potentially lower cost than a very short optical activecable, the copper cable may more easily provide the power to the centralcable run. FIG. 13A shows the arrangement where such power is carried bya dedicated conductor pair, whereas FIG. 13B shows the power transferredover one of the high speed signaling pairs.

While FIGS. 13A and 13B show the short copper connections as a male tofemale connector arrangement, which directly connects to a standard maleto male central cable, it should be obvious to one skilled in the artsthat the adapter arrangements illustrated in FIGS. 3 and 4 may besimilarly employed. Similarly, it should also be cleared thatimplementations in FIGS. 6 and 7 which employee retimers for addedjitter reduction are also possible and with the same potentialadvantages.

Thus, the user need not be concerned about choosing whether copper-basedsolutions or optical solutions are more appropriate, and then choose toconfigure the system with the appropriate ports. Instead, the user mayjust plug in the cable, and enjoy all of the benefits of opticalcommunication such as, for example, high bandwidth communication withlow power consumption and high port density, and with lesspre-processing and post-processing of information. Alternatively, theuser could choose a copper based version of the cable for particularlyshort links (say from the top to the bottom of a rack of switchingequipment) if economically advantageous.

A useful variation of these optical link cables with electricalinterface is the possibility of carrying more than one bidirectionalsignal in a single cable. In particular, the size of the opticalsubassemblies, the low power dissipation possible and the density ofpinout may allow the relatively easy implementation of two links withina connector width of approximately less than one half inch, or roughlythe size of the very common RJ-45 network connector. For example, asshown in FIG. 14A, the electrical connector 811 is defined with two setsof differential input and outputs (e.g., RX, RX2, TX and TX2) eachrepresenting independent bidirectional links, and the connector end maythen contain two sets of TOSAs 1413 and 1414 and/or ROSAs 1415 and 1416,which in turn are connected to 4 separate fibers 1431 through 1434.Alternatively, the two channels may be integrated in a single TOSA witha dual channel laser driver and two VCSELS, either discrete or on thesame subassembly. It will be apparent to one skilled at the art afterhaving read this description that the principle of having two (or more)channels in a cable may be applied to all the variants of the cablesdescribed above as well as to the various means of interconnectingcables directly or through a separate adapter. Two sets of TOSAs 1423and 1424 and ROSAs 1425 and 1426 may be included in the other end of thecable as well, thus establish a dual link duplex active cable 1400A. Itshould be clear that implementations with more than 2 links in a singleassembly are also possible.

FIG. 14B illustrates an embodiment that is similar to FIG. 14A in thatone end 1459 supports two independent channels, but somewhere along itslength 1465, the cable splits into two single channel cables 1466 and1467, each terminating in a single channel connector 1473 and 1483,respectively, each having a single TOSA and ROSA. For instance, cableend 1473 may be received by receptacle 1472 and includes TOSA 1474 andROSA 1475, whereas cable end 1483 may be received by receptacle 1482 andinclude TOSA 1484 and ROSA 1485. Each TOSA 1474 and 1484 is connectedthrough a respective optical fiber 1462 and 1461 to a corresponding ROSA1456 and 1455 in the dual link end 1459 of the cable 1400B. Each ROSA1475 and 1485 is connected through a respective optical fiber 1463 and1464 to a corresponding TOSA. The electrical connector 1451 of the duallink end 1459 of the cable is received by the electrical receptacle 1452of the host. Note that the host transmits two differential high speeddata signals TX and TX2, and receives two differential high speed datasignals RX and RX2.

Finally, there are a number of characteristics of the electricalconnector system which would be favorable for such an application.First, there might be a latching mechanism such as the tab style latchfound in an RJ-45 style connector or a push-pull style latch employed inthe SC style fiber optic connector.

Second, the receptacle on the host system may include provisions forvisual indicators of link activity and other status. This may beaccomplished by two means common in the RJ-45 connector system. Thefirst is inclusion of LEDs in the front panel face of the hostreceptacle with electrical connections to the host PCB. A second methodis to include plastic light pipes within the receptacle assembly toguide light from LEDs on the host PCBA to the front surface of thereceptacle.

Third, the cable may have a provision for some sort of keying system toallow or prevent different types of host systems from beinginterconnected. One example where a keying system would be important isto prevent the insertion of a single link cable in a dual link port.Another example would be the prevention of the connection of two hostsystems running different protocols, though this could be detected byprotocol means themselves. For example, exactly the same cable may beuseful for Ethernet and Fiber Channel applications, yet a system'sadministrator running a datacenter with both types of equipment may wishto prevent the interconnection of these systems by simple mechanicalmeans. Of course color coding or other simple means could be used forthis purpose as well. Keying features on a connector often comprise amechanical protrusion on one of a set of locations on the hostreceptacle and corresponding slots on the cable plug, or vice versa.Examples of these features can be found in the definition of the HSSDC2connector (see Small Form Factor Committee document SFF-8421 rev 2.6,Oct. 17, 2005).

There are many possible choices for the electrical connector in terms ofthe number of pins, their function and their relative arrangement.

FIG. 15A shows one possible pin arrangement involving 11 contacts, bothfrom the view of the cable plug end (top) as well as looking into thehost receptacle (bottom). Some pins are necessary for any implementationsuch as the power for the near end circuitry, Vcc, the groundconnections, Vee, the high speed differential transmit signals, TX+ andTX− and the high speed differential receive signals, RX+ and RX−. Otheroptional signals of use in some implementations are a separate powerconnection for far end power connections, VccF, a Fault/Interrupt pin,F/INT to indicate any problems with the link, and in the case of theInterrupt function, to prompt the host to query for more information, aserial data interface. In this case, a pair of pins representing aserial data line SDA and an associated serial data clock SCK such asused in the I2C communication system.

The far end power connection, VccF has been described previously asproviding an isolated or alternative voltage to supply the activecomponents within or beyond the far end of the cable, primarily forapplications which concatenate multiple cables in the various mannersdescribed above.

FIG. 15B shows a slightly different but important simplified pinout withonly 9 connections. In this case, there are no separate connections fora serial data interface. Nevertheless it possible to still thoseconnections over one of the set of high speed data pins through variouspossible means. These include, but are not limited to common modesignaling of the low speed interface on the differential high speedlines, or modulation of the low speed interface below the low frequencycut-on of the high speed data frequency content (which is typicallymodulated to achieve DC balance with no appreciable signal content belowa given frequency typically now lower than about 30 kHz for theseapplications).

The seeming disadvantage of not having separate pins for the serial datapath or the complexity of combining the low and high speed paths may bemore than offset by the savings in the connector design by reducing tothe minimum possible pin count.

FIG. 15C shows one possible pin arrangement for a single channel cableusing a 20 contact connector. This particular physical arrangement ofpin contacts is of interest because it is based on the same layout asthe PCB edge connector of the SFP and XFP form factors which have beenproven to have good performance at 10 G serial data rates.

While numerous arrangements of these pins may be practical, FIG. 15Cillustrates high speed pairs TX+, TX−, RX+ and RX− are surrounded byground lines Vee, which is useful both in achieving the desiredimpedance (for example 100 Ohms differential) of the differential lines,as well as reducing crosstalk between high speed lines. Several linesRes are shown as reserved for future functions. Two-wire interface lines(SDA) and (SCL) may provide serial data to the electrical connector forcontrolling the optics and for other desired functions.

FIG. 15D shows a similar pin arrangement, but one designed for cablescarrying two full duplex links. Specifically, pins TX2+, TX2−, RX2+ andRX2− are used for a second duplex link, as well as a separate Fault lineF/INT2. Finally, FIG. 15E shows a 22 pin arrangement for a dual linkwhich differs from FIGS. 15C and 15D in that it provides more groundseparation between the high speed pairs. It should be obvious to oneskilled in the arts that a simplified version for a single link can bederived from FIG. 15C and that certain aspects of the arrangements arearbitrary.

Thus, the cable permits high-speed communication using optics while notrequiring that the network nodes interface with the cable using optics.Instead, the user may simply plug the cable into electrical connections.The cable may also include additional functionality to improve theperformance and safety of the cable.

FIG. 16 illustrates a view of one end 1600 of one embodiment of a singlelink active cable. A top part of the shell 1601 is cut away forillustrative purposes so that the internals of the end 1600 may beviewed. The end 1600 has 10 electrical traces 1602 disposed on each sideof printed circuit board 1610, allowing for a total of 20 electricaltraces. In this case, the PCB edge contact design is the same as that inthe existing SFP form factor standard, though that is not a requirementof such a design. Thus, the end 1600 may support the connectionconfigurations of FIG. 15C or 15D. The end 1600 includes ROSA 1603 andTOSA 1604, which are coupled to the corresponding receive optical fiber1605 and the transmit optical fiber 1606 via ferrules 1607 and 1608,respectively. The optical fibers 1605 and 1606 form part of cable 1609,which is protected by the cable jacket. The cable typically would alsoincorporate a strength member such as Kevlar yarn which would beanchored to the interface between the external portion of the cable andthe plug shell.

FIG. 17A illustrates a view of one end 1700 of an embodiment of a duallink fully-duplex active cable. Once again, the top part of the shell1701 is cut away for illustrative purposes. The end 1700 has 10electrical traces disposed on each side of an electrical connector 1702portion of the printed circuit board 1709, allowing for a total of 20electrical traces. Thus, the end 1700 may support the connectionconfigurations of FIGS. 15C and 15D. However, another electrical tracecould be added to each side of the electrical connector 1702 to permit atotal of 22 traces to thereby support the connection configuration ofFIG. 15E. The end 1700 includes ROSA 1703 and TOSA 1704, which arecoupled to a corresponding receive optical fiber 1705 and the transmitoptical fiber 1706 via ferrules 1707 and 1708, respectively, on one sideof the printed circuit board 1709. Symmetrically, another set of ROSAand TOSAs is disposed on the far end of the support board, though notshown in this illustration, which may be similarly coupled tocorresponding fibers 1715 and 1716 via corresponding ferrules. Theoptical fibers 1705, 1706, 1715 and 1716 form part of cable 1719, whichis protected by the cable jacket.

FIG. 17B illustrates a perspective view of the end 1700 of FIG. 17A,only with the shell 1701 entirely removed. Here, the ROSAs on both sidesof the printed circuit board may be viewed. The TOSA on the far end ofthe printed circuit board is still not viewable, but it may be simplyplaced opposite the respective ROSA on the near side of the printedboard. FIG. 17C illustrates another perspective view of the end 1700 ofFIG. 17A.

FIG. 18 illustrates a view of one end 1800 of an embodiment of a singlelink fully-duplex active cable, with its protective shell removed foreasier visualization. The electrical connectors 1802 may be similar tothe electrical connectors 1602 of FIG. 16. Here, the laser driver andpost amplifier are integrated into a single integrated circuit 1810. AnEEPROM, which might be used to store setup or serial ID information,could be mounted on the far side of the printed circuit board. The end1800 includes ROSA 1803 and TOSA 1804, which are coupled to thecorresponding receive optical fiber 1805 and the transmit optical fiber1806 via ferrules 1807 and 1808, respectively. The optical fibers 1805and 1806 form part of cable 1809, which is protected by the cablejacket.

FIG. 2C above illustrated how a variant of the optical cable with anoptical interface compliant with optical link standards could be used tointerconnect a host system with an electrical active cable receptacle toanother system with an industry standard optical transceiver. This veryuseful application can also be achieved through the use of an adapterwhich plugs into the cage system of a standard form factor opticaltransceiver and which satisfies all the signaling requirements of thatinterface. In addition to connecting a system with a dedicated activecable receptacle to that with an industry standard optical transceiver,two such adapters could be used to interconnect any present day systemswith such industry standard transceivers. In general, such adapters maysatisfy the mechanical electrical signaling requirements of the variousform factor standards which have generally been established throughmultisource agreements in the industry (references above).

FIG. 19 illustrates a signal mapping diagram of an adaptor 1900 thatadapts between the common SFP standard and the active cable signalsillustrated with respect to FIGS. 15A-C. On the left side of the adaptor1900 are the standard SFP signals 1901A coupled to an SFP connectorabstractly represented by reference number 1902A. On the right of theadaptor 1900 are the active signals 1901B of FIG. 15A-15C coupled to theactive cable connector abstractly represented by reference number 1902B.The adaptor 1900 may include an optional power conditioner 1903 if powerregulation is needed between the SFP power supply Vcc and the activecable power supply VccF.

FIG. 20A illustrates a first embodiment of a mechanical design of an SFPto active cable adaptor. Here, a shell is shown protecting hiddeninternal circuitry and components. The proximate end of the adaptorshows the electrical receptacle for the active cable, with a latch bailto actuate the retention mechanism of the overall adapter (a standardfeature of the SFP mechanical interface). A separate latch mechanism,[Shown only as a small catch in the view FIG. 20B] is provided forretaining the cable to the adaptor. Several contacts are shown whichcontact the respective electrical traces of the active cable end whenthe active cable is inserted into its corresponding electricalreceptacle on the adaptor. EMI spring are shown that ensure electricalcontact of the shell to the host, to thereby ensure that the shellcarries a voltage that at least partially prevents electromagneticemissions from the host system or adaptor itself from exiting thesystem.

FIG. 20B illustrates another perspective view of the mechanism design ofthe adaptor of FIG. 20A. Here, the SFP end of the adaptor is shown indetail. The SPF end includes a Printed Circuit Board (PCBA) that hasmultiple electrical contacts suitable for reception of anySFP-compliance connector. An SFP latch is also shown, which complieswith the SFP standard.

FIG. 20C illustrates a top perspective view of the adaptor with more ofits shell cut-away to expose the various components on the upper surfaceof the printed circuit board including electrical traces from the SFPelectrical connector, and the signal mapping component 2002. The signalmapping component 2002 mechanically receives the active cable so as tobe electrically coupled to the active cable, and is electricallyhardwired to the SFP traces. The mapping component 2002 may performappropriate signal mapping, an example of which being illustrated inFIG. 19. FIG. 20D illustrates a bottom perspective view of the adaptorwith more of its shell cut away to expose the various components of thelower surface of the printed circuit board

FIG. 21 illustrates a signal mapping diagram of an adaptor 2100 thatadapts between the common XFP standard and the active cable signalsillustrated with respect to FIG. 15A-15C. On the left side of theadaptor 1500 are the standard XFP signals 2101A coupled to an XFP edgeconnector abstractly represented by reference number 2102A. On the rightof the adaptor 2100 are the active signals 2101B of FIG. 15A-15C coupledto the active cable connector abstractly represented by reference number2102B. The adaptor 2100 may include an optional power conditioner 2103if power regulation is needed between the XFP power supply Vcc and theactive cable power supply VccF.

The XFP standard requires a retiming function which may be included inthe adaptor and is illustrated in FIG. 21 as the two optional CDRblocks. However it may provide a useful cost and power savings toeliminate the retiming function. This may be acceptable if the activecable sufficiently limits jitter because of the choice of fiber, lengthor any of the number of active jitter reductions described previously,such as jitter precompensation.

FIG. 22A illustrates a view of first embodiment of a mechanical designof an XFP to active cable adapter. The proximate end of the adaptorshows the electrical receptacle for the active cable, with a latch bailto actuate the retention mechanism of the overall adapter (a standardfeature of the XFP mechanical interface, which in this illustration isimplemented as two sliding latch features on the sides, only one ofwhich is visible). A separate latch mechanism (shown only as a smallcatch in the view FIG. 22A) is provided for retaining the cable to theadaptor. Several contacts are shown which contact the respectiveelectrical traces of the active cable end when the active cable isinserted into its corresponding electrical receptacle on the adaptor.

FIG. 22B illustrates another perspective view of the design of theadaptor in FIG. 16A. This view shows part of the XFP to host interfaceon the internal PCBA.

FIG. 22C illustrates a top perspective with a portion of the shellcut-away to expose features of the internal design, particularly thelayout of the top of the PCBA. High speed signals from the XFP edgeconnector are routed directly to and from a TX and RX CDR respectively.The output of the TX CDR is directly tied to the TX pins of the activecable electrical receptacle. Similarly, high speed lines from thereceive pins of the active cable receptacle are coupled to the RX CDR.

FIG. 22D shows a bottom perspective view of the adapter with the bottomshell cover removed. This view illustrates connection of the various lowspeed status and control lines through a microcontroller to adapt themto the related signals used by the active cable receptacle while at thesame time the expectation of the host system for the responses fromthese connections. The microcontroller can similarly provide EEPROM toprovide an appropriate response to a serial ID query from the host. Alsoshow in FIG. 22D are the various power supply connections for the 3.3Vand 5.0V supplies as well as the previously discussed APS supply.

The final type of adaptor discussed is for use in X2 receptacles. The X2is one of three form factors which implement a XAUI (10 GigabitAttachment Unit Interface) electrical interface, the other two being theXENPAK and XPAK form factors. The host side electrical interface ofthese three designs is essentially identical and they differ only inmechanical features.

FIG. 22 illustrates a signal mapping diagram of an X2 to active cableadapter. The main feature of the XAUI interface is that the overall 10 Gdatastream is carried over four lower speed connections in eachdirection (labeled as RX+/−0-3 and TX+/−0-3). Because the four XAUIlines uses a different signal coding format than the 10 G serialconnections, the actual transition rate is somewhat higher than aquarter of the rate of the serial interface. In addition to the parallelelectrical interface, the XAUI standard requires jitter reduction,retiming and recoding the signals before transmission as a signal, asvary as a wide range of low speed control and monitoring signals.Presently, most of these features have been implemented in a single ICcommonly known as a XAUI SERDES (serialiser-deserialiser) and shown inFIG. 17

Another feature of the XAUI interface is an adjustable power supply,labeled APS on the pin connections in FIG. 23. This special connectionis for an adjustable power supply on the host system for which thevoltage is set by a resistor to ground inside the X2 module (or in thiscase adapter) connected to a pin labeled APS SET. A third related pinlabeled APS sense carries an internal measurement of the APS voltageback to the host system as part of the voltage control feedback loop. Inthe present embodiment, this adjustable power supply is only used forpowering the XAUI SERDES itself, typically a low voltage CMOS IC.

FIG. 24A illustrates a view of first embodiment of a mechanical designof an X2 to active cable adapter. The proximate end of the adaptor showsthe electrical receptacle for the active cable, with a latch release toactuate the retention mechanism of the overall adapter (a standardfeature of the X2 mechanical interface, which in this illustration isimplemented as two retracting latch features on the sides, only one ofwhich is visible). A separate latch mechanism, (not shown) is providedfor retaining the cable to the adaptor. Several contacts are shown whichcontact the respective electrical traces of the active cable end whenthe active cable is inserted into its corresponding electricalreceptacle on the adaptor.

FIG. 24B illustrates another perspective view of the design of theadaptor in FIG. 24A. This view shows part of the X2 to host interface onthe internal PCBA.

FIG. 24C illustrates a top perspective with a portion of the shellcut-away to expose features of the internal design, particularly thelayout of the top of the PCBA. Four sets of XAUI signal differentialpairs are routed in each direction from the X2 edge connector are routeddirectly to and from the XAUI SERDES. The TX output of the XAUI SERDESis directly tied to the TX pins of the active cable electricalreceptacle. Similarly, high speed lines from the receive pins of theactive cable receptacle are coupled to the RX input of the XAUI SERDES.Also shown in FIG. 24 is a crystal oscillator (labeled XTAL). This isnormally required to provide the timing basis of the transmitted serialsignal.

FIG. 24 shows a bottom perspective view of the adapter with the bottomshell cover removed. This view illustrates connection low speed statusand control lines to and from the XAUI SERDES which used to adapt themto the related signals used by the active cable receptacle while at thesame time the expectation of the host system for the responses fromthese connections. The SERDES will provide an interface to EEPROM toprovide an appropriate response to a serial ID query from the host. Alsoshow in FIG. 2418D are the various power supply connections for the 3.3Vand 5.0V supplies as well as the previously discussed APS supply.

Accordingly, an active cable is described in which an electricalconnection is provided on at least one side of the cable to receive thehigh speed electrical signal, while having the signal being communicatedoptically through most of the cable length. An adaptor for adaptingbetween SFP, XFP or X2 and the active cable connector has also beendescribed.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

1. An integrated cable comprising: a first optical fiber within theintegrated cable, the first optical fiber having a first end and asecond end; a first electrical connector integrated with the integratedcable, the first electrical connector configured to connect with a firstelectrical port external to the integrated cable such that whenconnected to the first electrical port the first electrical connector isconfigured to receive a first electrical signal and provide the firstelectrical signal to a first electro-optical transducer; the firstelectro-optical transducer disposed within the integrated cable andcoupled to the first end of the first optical fiber such that when thefirst electro-optical transducer receives the first electrical signaland converts the first electrical signal into a first optical signal thefirst optical signal is coupled to the first end of the first opticalfiber; a second electrical connector integrated with the integratedcable, the second electrical connector configured to connect with asecond electrical port external to the integrated cable; a firstopto-electrical transducer disposed within the integrated cable andcoupled to a second end of the first optical fiber such that when thefirst opto-electrical transducer receives the first optical signal fromthe second end of the first optical fiber the first opto-electricaltransducer converts the first optical signal to a second electricalsignal and provides the second electrical signal to the secondelectrical connector such that when connected to the second electricalport the second electrical connector is configured to provide the secondelectrical signal to the second electrical port; and a circuit disposedin the integrated cable, the circuit configured to provide pre-emphasisof the second electrical signal.
 2. An integrated cable in accordancewith claim 1, wherein the pre-emphasis is accomplished by eitherboosting high frequency content or removing low frequency content fromthe first or second electrical signals.
 3. An integrated cable inaccordance with claim 1, further comprising: a mechanism for providinghost selection of a pre-emphasis setting.
 4. An integrated cable inaccordance with claim 3, wherein the preemphasis setting is hostselectable via a serial interface of the integrated cable.
 5. Anintegrated cable in accordance with claim 4, wherein the serialinterface is I2C.
 6. An integrated cable in accordance with claim 1,wherein the preemphasis is configured to compensate for high frequencyrolloff of the host electrical traces.
 7. An integrated cable inaccordance with claim 1, wherein the selection of the pre-emphasisdepends on a length of an electrical interconnect between the first orsecond electrical ports and IC elements of the host.
 8. An integratedcable in accordance with claim 1, further comprising circuitryconfigured to provide equalization of the first electrical signal withinthe integrated cable.
 9. An integrated cable in accordance with claim 8,wherein the equalization is fixed, adjustable, or adaptableequalization.
 10. An integrated cable in accordance with claim 9,wherein the equalization is adjustable.
 11. An integrated cable inaccordance with claim 10, wherein the adjustable equalization is hostselectable via a serial interface of the integrated cable.
 12. Anintegrated cable in accordance with claim 11, wherein the serialinterface includes I2C.
 13. An integrated cable in accordance with claim8, wherein the equalization is configured to compensate for highfrequency rolloff of the host electrical traces.
 14. An integrated cablein accordance with claim 8, wherein the equalization is automaticallyadaptive to host impairments.
 15. An integrated cable in accordance withclaim 1, further comprising memory in the integrated cable.
 16. Anintegrated cable in accordance with claim 15, the integrated cableincluding a serial data interface configured to read or write data tothe memory.
 17. An integrated cable in accordance with claim 16, whereinthe serial data interface is configured to communicate diagnosticinformation from the integrated cable.
 18. An integrated cable inaccordance with claim 16, wherein the serial data interface includesI2C.
 19. An integrated cable in accordance with claim 1, furthercomprising: a second optical fiber within the integrated cable fortransmitting optical signals in the same direction as the first opticalfiber, the second optical fiber having a first end and a second end; thefirst electrical connector configured to receive a third electricalsignal and provide the third electrical signal to a secondelectro-optical transducer; the second electro-optical transducerdisposed within the integrated cable and coupled to the first end of thesecond optical fiber such that when the second electro-opticaltransducer receives the third electrical signal and converts the thirdelectrical signal into a second optical signal the second optical signalis coupled to the first end of the second optical fiber; and a secondopto-electrical transducer disposed within the integrated cable andcoupled to a second end of the second optical fiber such that when thesecond opto-electrical transducer receives the second optical signalfrom the second end of the second optical fiber the secondopto-electrical transducer converts the second optical signal to afourth electrical signal and provides the fourth electrical signal tothe second electrical connector such that when connected to the secondelectrical port the second electrical connector is configured totransmit the fourth electrical signal to the second electrical port. 20.An integrated cable in accordance with claim 1, further comprising: asecond optical fiber within the integrated cable for transmittingoptical signals in the opposite direction as the first optical fiber,the second optical fiber having a first end and a second end; the secondelectrical connector configured to receive a third electrical signal andprovide the third electrical signal to a second electro-opticaltransducer; the second electro-optical transducer disposed within theintegrated cable and coupled to the second end of the second opticalfiber such that when the second electro-optical transducer receives thethird electrical signal and converts the third electrical signal into asecond optical signal the second optical signal is coupled to the secondend of the second optical fiber; and a second opto-electrical transducerdisposed within the integrated cable and coupled to the first end of thesecond optical fiber such that when the second opto-electricaltransducer receives the second optical signal from the first end of thesecond optical fiber the second opto-electrical transducer converts thesecond optical signal to a fourth electrical signal and provides thefourth electrical signal to the first electrical connector such thatwhen connected to the first electrical port the first electricalconnector is configured to transmit the fourth electrical signal to thefirst electrical port.
 21. An integrated cable comprising: a firstoptical fiber within the integrated cable, the first optical fiberhaving a first end and a second end; a first electrical connectorintegrated with the integrated cable, the first electrical connectorconfigured to connect with a first electrical port external to theintegrated cable such that when connected to the first electrical portthe first electrical connector is configured to receive a firstelectrical signal and provide the first electrical signal to a firstelectro-optical transducer; the first electro-optical transducerdisposed within the integrated cable and coupled to the first end of thefirst optical fiber such that when the first electro-optical transducerreceives the first electrical signal and converts the first electricalsignal into a first optical signal the first optical signal is coupledto the first end of the first optical fiber; a second electricalconnector integrated with the integrated cable, the second electricalconnector configured to connect with a second electrical port externalto the integrated cable; a first opto-electrical transducer disposedwithin the integrated cable and coupled to a second end of the firstoptical fiber such that when the first opto-electrical transducerreceives the first optical signal from the second end of the firstoptical fiber the first opto-electrical transducer converts the firstoptical signal to a second electrical signal and provides the secondelectrical signal to the second electrical connector such that whenconnected to the second electrical port the second electrical connectoris configured to provide the second electrical signal to the secondelectrical port; and circuitry configured to provide equalization of thefirst electrical signal within the integrated cable.
 22. An integratedcable in accordance with claim 21, wherein the equalization is fixed,adjustable, or adaptive equalization.
 23. An integrated cable inaccordance with claim 22, wherein the equalization is adjustable.
 24. Anintegrated cable in accordance with claim 23, wherein the adjustableequalization is host selectable via a serial interface of the integratedcable.
 25. An integrated cable in accordance with claim 24, wherein theserial interface includes I2C.
 26. An integrated cable in accordancewith claim 21, wherein the equalization is configured to compensate forhigh frequency rolloff of the host traces.
 27. An integrated cable inaccordance with claim 21, wherein the equalization is automaticallyadaptive to host impairments.
 28. An integrated cable in accordance withclaim 21, further comprising: a second optical fiber within theintegrated cable for transmitting optical signals in the same directionas the first optical fiber, the second optical fiber having a first endand a second end; the first electrical connector configured to receive athird electrical signal and provide the third electrical signal to asecond electro-optical transducer; the second electro-optical transducerdisposed within the integrated cable and coupled to the first end of thesecond optical fiber such that when the second electro-opticaltransducer receives the third electrical signal and converts the thirdelectrical signal into a second optical signal the second optical signalis coupled to the first end of the second optical fiber; and a secondopto-electrical transducer disposed within the integrated cable andcoupled to a second end of the second optical fiber such that when thesecond opto-electrical transducer receives the second optical signalfrom the second end of the second optical fiber the secondopto-electrical transducer converts the second optical signal to afourth electrical signal and provides the fourth electrical signal tothe second electrical connector such that when connected to the secondelectrical port the second electrical connector is configured totransmit the fourth electrical signal to the second electrical port. 29.An integrated cable in accordance with claim 21, further comprising: asecond optical fiber within the integrated cable for transmittingoptical signals in the opposite direction as the first optical fiber,the second optical fiber having a first end and a second end; the secondelectrical connector configured to receive a third electrical signal andprovide the third electrical signal to a second electro-opticaltransducer; the second electro-optical transducer disposed within theintegrated cable and coupled to the second end of the second opticalfiber such that when the second electro-optical transducer receives thethird electrical signal and converts the third electrical signal into asecond optical signal the second optical signal is coupled to the secondend of the second optical fiber; and a second opto-electrical transducerdisposed within the integrated cable and coupled to the first end of thesecond optical fiber such that when the second opto-electricaltransducer receives the second optical signal from the first end of thesecond optical fiber the second opto-electrical transducer converts thesecond optical signal to a fourth electrical signal and provides thefourth electrical signal to the first electrical connector such thatwhen connected to the first electrical port the first electricalconnector is configured to transmit the fourth electrical signal to thefirst electrical port.